In modern times, one thing that can almost always be taken for granted is that when a handset of an active land-based telephone is picked up or turned on, a dial tone is heard. For years, telecommunications network operators have been required by law to maintain a high-degree of reliability of their networks in order to maintain their licenses. Because of the high-degree of reliability, users have become accustomed to picking up the handset and hearing the familiar dial tone, which is generally formed of multiple, continuous frequencies. Despite recent developments in telecommunications, such as voice over internet protocol (VoIP) and mobile telephones, the concept of a dial tone is nearly universally known.
While different types of telephones and different networks around the world may differ in the sound of the dial tone and method of producing the dial tone, most non-cellular networks have some version of a dial tone. Where the traditional public switched telephone network (PSTN) may receive the dial tone from a switch, such as a class 5 switch on the PSTN, the VoIP dial tone may be generated within an adaptor connected to the phone on a user's end.
FIG. 1 is an illustration of a conventional telephone communications system 100 and depicts a calling telephone 102 and a receiving telephone 104 being in communication through a network 106. The network 106 may be the PSTN.
FIG. 2 is timing diagram of an exemplary process 200 for establishing a traditional call between a calling phone 202 and called phone 204 over a network switch 206. The calling phone 202 is shown being picked up by a user at 207. Time period 208 is the time that a dial tone is sent from the switch 206 to the calling phone 202. As well understood in the art, time period 207 is defined as the time between when the calling phone 202 goes “off hook” (i.e., when a user picks a handset off the receiver or turns on a cordless handset) and when a telephone call is initiated or, in the case of using a business telephone, a function key is pressed by a user. To initiate a call, the calling party may dial a telephone number of a called party. Dual-tone multiple frequency (DTMF) tones may be sent to network switch 206 at step 210. The network switch 206, in response, sends a connect signal and a ring signal 212 to the called phone 204. A ring-back signal 214 may then be sent from the network switch 206 to the calling phone 202 during the time that the signal 212 is ringing the called phone 204. In response to a user picking up 216 the called phone 204, a connect signal 218a is sent from the called phone 204 to the network switch 206, which, in turn, sends connect signal 218b back to the calling phone 202, thereby completing the connection.
FIG. 3 is a timing diagram showing a conventional call initiation process 300. Shown are a calling phone 302 and network switch 304. A user may take the calling phone 302 off-hook by picking up a handset at step 306. An off-hook signal 308 is communicated from the calling phone 302 to the network switch 304. In response, the network switch 304 communicates a dial tone signal 310 back to the calling phone 302. The dial tone signal is generally continuously sent until a user initiates a call by pressing a keypad button or other call or function initiation mechanism or until a predetermined time has elapsed, where upon the dial tone is substituted with an off-hook tone. A DTMF signal 312 is thereafter communicated to the network switch 304 from the calling phone 302 and the dial tone signal is terminated.